The present invention relates generally to signal processing parameters for processing received signals in a wireless communication system, and more particularly to estimating signal impairment correlations of multiple images of the received signals.
Wireless receivers in spread spectrum systems, such as code division multiple access (CDMA) systems, are well known in the communication arts. Typically, wireless receivers operating in a spread spectrum system include a RAKE receiver, which is responsible for demodulating multiple signal images of a received multi-path signal. In general, a RAKE receiver in a base station or a mobile station receives a desired signal in the presence of other interfering signals intended for or sent from other base stations and/or mobile stations. By using calculated weighting factors to coherently combine correlated symbols corresponding to the desired received signal, the RAKE receiver uses multi-path reception to improve the signal-to-noise ratio (SNR) of the received multi-path signal.
While conventional RAKE receivers are effective at reducing channel path noise, receiver noise, etc., and therefore, are effective at improving the SNR of received multi-path signals, conventional RAKE receivers are typically ineffective against interference noise caused by self-interference, multi-user access interference, etc. To address noise and interference, a generalized RAKE (G-RAKE) receiver may be used instead of the conventional RAKE receiver, as discussed in co-assigned U.S. Pat. No. 6,363,104 to Bottomley entitled “Method and Apparatus for Interference Cancellation in a RAKE Receiver,” issued 26 Mar. 2002. This patent is incorporated herein by reference. Like a RAKE receiver, a G-RAKE receiver correlates received signal images, weights the correlated signal images using weighting factors, and coherently combines the weighted signal images. However, unlike the RAKE receiver, the weighting factors of the G-RAKE are based on estimated impairment correlations. To suppress noise and interference, the G-RAKE combiner uses impairment correlation based weighting factors to weight the correlated signal images and to coherently combine the weighted images. As discussed further below, the success of the interference suppression in a G-RAKE receiver is dependent on the accurate estimation of these impairment correlations.